Within digital communications systems, analog data signals are typically transmitted from a transmitter to a receiver through a suitable signal transmission medium that links the transmitter to the receiver, often referred to as a communication channel (hereafter referred to as “channel”). Generally, the physical layer (PHY) of a data communications interface (e.g., data network interface) of a computing device is responsible for transmitting data bits over the channel and, as such, comprise a transmitter, a receiver, or both compatible the channel. Channels vary and can include, for example, wired or wireless channels. For instance, a channel can comprise a cable with multiple twisted pairs (e.g., Category 5 (CAT 5) cable or a Category 6 (CAT 6) cable) or a cable with a single twisted pair. Channel type and the physical environment can determine the presence and severity of various channel effects (e.g., interference, attenuation, and delay) with respect to a given channel, which can have detrimental effects on an analog data signal transmitted over the given channel by the time the transmitted analog data signal reaches the receiver. Generally, the PHY layer of a communications interface compatible with a given channel can compensate for channel effects and achieve a certain level of data rate/speed (e.g., 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps, or 100 Gbps) by using different types of encoding or signal modulation schemes for transmitting data over the given channel and noise. In order to guarantee interoperability among various transceivers, the transmit specifications are typically defined by standard bodies such as the Institute of Electrical and Electronics Engineers (IEEE). An example IEEE standard includes the IEEE 802.3 standards, which standardizes the physical layers of various Ethernet protocols. Among other things, the standard may specify the transmit signal modulation, transmit filtering and precoding. The modulation may be a pulse amplitude modulation (PAM) scheme (e.g., PAM2 or PAM4), and transmit filtering and precoding may be linear or nonlinear.
With respect to a given channel, channel effects can distort (e.g., cause amplitude or phase distortion) analog signal transmitted by a transmitter (e.g., of a PHY), which in turn can result in inter-symbol interference (ISI) in the transmitted analog data signal received by the receiver (e.g., of a PHY). A pulse or other symbol in a transmitted analog data signal, representing the logic state of one data bit at a cursor, can be effectively distorted by ISI. ISI can comprise a pre-cursor component (pre-cursor ISI) that distorts a transmitted analog data signal with respect to one or more data bits preceding a bit corresponding to a cursor of the transmitted analog data signal, and a post-cursor component (post-cursor ISI) that distorts the transmitted analog data signal with respect to one or more data bits succeeding a bit corresponding to a cursor of the transmitted analog data signal. Traditionally, a receiver can implement decision feedback equalization (DFE) to correct for post-cursor ISI in the signal received at the receiver, and can include a linear equalizer to correct for pre-cursor ISI in a received analog data signal. Additionally, in some instances, a transmitter can implement precoding, such as Tomlinson-Harashima precoding (THP), to pre-compensate for channel effects by using signal equalization on the transmitter side prior to the transmitter transmitting an analog signal to a receiver.
While DFE provides effective equalization, it typically suffers from error propagation where a wrong detected symbol at receiver is fed back through a DFE, which increases the probability of more error symbols. The stronger the DFE coefficients, the higher the chance of error propagation. Tomlinson-Harashima Precoding is as effective as DFE in equalization. Unlike DFE, THP does not suffer from error propagation as the transmit symbols are readily available for the transmitter and the THP; hence there is no detection error. On the other hand, THP typically increases the effective resolution of the symbol in the transmit data path. While the input to THP may take a finite number of discrete values of PAM levels, the output of the THP may take any possible value within the output range. This can increase the complexity of the transmit driver at the transmitter, and can also increase the complexity of the echo and near-end crosstalk cancellers in full duplex and multichannel systems.
Though a high data rate is often desired for applications of data communication between a transmitter and a receiver, the physical environment between transmitter and receiver can limit the type of channel that can be used therebetween and, in turn, the type of channel can determine the types of data rates that can be achieved. For instance, the in use of sensors (e.g., cameras, motion, radar, etc.) and computing equipment within vehicles (e.g., smart and autonomous cars) has increased the importance of high-speed data communications (e.g., data networking) between electronic components within vehicles. However, the types of channels that can be used in vehicle environment applications can be limited. For example, issues relating to reliability, safety, security, or government regulation can render a wireless channel non-viable option for some vehicle environment applications, and can limit wired channel options that can be used for some vehicle environment application. Additionally, wired channel options in vehicle environments applications can be further limited by other factors, such as availability of physical space for wiring within a vehicle, power requirements needed for using certain types of wired channels, and weight or cost impact of wiring (e.g., a single twisted pair cable versus a multi-twisted pair cable) needed for certain types of wired channels. Accordingly, for data communication within certain physical environments (e.g., vehicle environments and aircraft environment applications), it would be beneficial to achieve the highest data communication speeds possible over wired channels that are already suitable or available (e.g., existing) within those physical environments.